Hydrocarbon Processing - September 2021 - 65

Process
Optimization
A. SAKA and D. KUTMAN, Tüpraş, İzmit, Turkey
Management of LPG pool in a complex refinery
LPG pool management is becoming more important as the
regulations on the product specifications tighten. If this pool is
managed unwisely, it can lead to throughput reduction or even
unit shutdown.
At Tüpraş' İzmit refinery, LPG is produced in three crude
distillation units (CDUs), one fluid catalytic cracking unit
(FCCU), one delayed coking unit (DCU), two Platformers,
one diesel hydrotreating unit (DHTU) and two hydrocracking
units (HCUs). Some of these LPG products are sent directly to
storage tanks, while others require posttreatment. Three LPG
treaters help meet sulfur-based specifications, and a C3
/C4
splitter is followed by a selective hydrogenation unit (SHU) to
meet butadiene specifications. Additionally, an LPG recovery
compressor with a chiller and an LPG evaporator is used, according
to production planning requirements.
Eight production/sales spherical tanks and three bullet
tanks for off-specification LPG product are managed without
interrupting production and sales activities. Storage tanks are
connected to one another, to jetties and to customer pipelines
for sales and loading/unloading activities.
The aim of this article is to define how to manage a complex
LPG pool of 10 sources with different specifications for purity,
butadiene content, total sulfur and evaporation residue. Ways
of coping with different pool challenges due to upsets and unit
shutdowns are described.
LPG product specifications. Automotive gas and LPG are
comprised of propane, propylene, butane, butane isomers, butene
and traces of other hydrocarbons.1
Product specifications
for automotive gas and LPG are defined according to EN-589
directives. Limitations are defined for motor octane number
(MON); total dienes content including 1,3 butadiene; hydrogen
sulfide (H2
S); total sulfur content after odorization; copper
strip corrosion; evaporation residue; vapor pressure gauge at
40°C; vapor pressure gauge at minimum 150 kPa at five temperature
grades; water content; and odor (TABLE 1).
In 2019, the EN-589 automotive gas and LPG specification
was revised to incorporate a maximum 1,3 butadiene content of
0.1 m/m. The specification for propane content was proposed
to be changed from a volume basis to a mass basis, to be applied
in two steps: first 20% and then 30%. However, consensus was
not achieved on 30% propane content, so this revision was postponed
for further evaluation. A final change for the LPG specification
is maximum total sulfur content, which was decreased
from 50 mg/kg to 30 mg/kg.
LPG pool. The general configuration of LPG production at the
İzmit refinery is shown in FIG. 1. LPG from the DCU, FCCU,
CDU1, CDU2 and CDU3 are rich in H2
S and mercaptans. They
must be treated in LPG Merox units (Merox 1, Merox 2 and Merox
3). The DCU LPG can be treated in both Merox 1 and Merox 3.
The DCU and FCCU LPG products are rich in butadiene content.
The butadiene-containing, sulfur-treated LPG from Merox
1 and Merox 3 are sent to a downstream unit-a combination of
a C3
and C4
can be stored separately.
The rest of the LPG produced in Platformer 1, Platformer
2, the DHP, HCU1 and HCU2 normally does not require LPG
TABLE 1. LPG specifications1
Limits
Property
MON
Total dienes content, %m/m
1,3 butadiene, %m/m
Propane content from April 1,
2021 will be evaluated, %m/m
H2
S
Total sulfur content
(after odorization), mg/kg
Copper strip corrosion,
(hr at 40°C), rating
Evaporation residue,
mg/kg
Vapor pressure gauge
at 40°C, kPa
Vapor pressure gauge at
minimum 150 kPa at five
temperature grades:
Grade A, °C
Grade B, °C
Grade C, °C
Grade D, °C
Grade E, °C
Water content
Odor
Pass
Unpleasant and
distinctive at 20% LFL
Class 1
60
1,550
20
30
Negative
30
Minimum Maximum
89
0.5
0.1
Test method
Annex B
EN 27941
DIN 51619
DIN 51619
EN 27941
DIN 51619
EN ISO 8819
EN 17178
ASTM D6667
EN ISO 6251
EN 15470
EN 15471
EN 16423
EN ISO 4256
EN ISO 8973
and Annex C
EN ISO 8973
and Annex C
-10
-5
10
20
EN 15469
See 6.3 and
Annex A
Hydrocarbon Processing | SEPTEMBER 2021 65
/C4 splitter and a selective hydrogenation unit (SHU)-to
meet butadiene specifications. After passing through the C3/C4
splitter, the C3
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